1. Field of the Invention
The invention relates to a nonvolatile memory device and method for fabricating the same, and more particularly, relates to a control gate insulating layer of a nonvolatile memory device and method for fabricating the same.
2. Description of the Related Art
A flash memory is a type of non-volatile memory. Generally speaking, a flash memory comprises two gates, the first gate is a floating gate for data storage and the second gate is a control gate for data input/output. The floating gate is placed under the control gate and “floats”. Note that “floating”, refers to isolating the floating gate and surrounding it with insulating materials for preventing charge loss. The control gate is connected to a word line (WL) for device control. One advantage of flash memories is block-by-block erasing. Flash memories are widely used in consumer electronic products, for example, digital cameras, digital videos, mobile phones, desktops, mobile audio players and personal digital assistants (PDA).
FIG. 1 illustrates a conventional nonvolatile memory device 150. The conventional nonvolatile memory device 150 mainly comprises a common-used control gate 110 and a pair of floating gates having a first floating gate 104a and a second floating gate 104b. Inter-gate insulating layers 106a and 106b are located between the control gate 110 and the first floating gate 104a and the second floating gate 104b, respectively. A control gate insulating layer 108 is located between the control gate 110 and a substrate 100. The conventional control gate insulating layer 108 formed by, for example, thermal oxidation process usually has non-uniform thickness. For example, the central portion of the conventional control gate insulating layer has a thickness larger than a thickness of the marginal region of the control gate insulating layer. When a high voltage is applied to the control gate to program or erase data stored in the floating gate, a malfunction, for example, early breakdown, occurs at the thinner control gate insulating layer region, hindering electrical performances or device reliability.
Thus, a novel nonvolatile memory device with a uniform control gate insulating layer is needed.